Sabo Dam Research Articles

Consideration of the causes of the destruction of the wing of Sugawa Daiichi sabo dam during heavy rainfall in the northern part of Kyushu Island, July 2017

Consideration of the causes of the destruction of the wing of Sugawa Daiichi sabo dam during heavy rainfall in the northern part of Kyushu Island, July 2017

Load reduction mechanism analysis of energy dissipators at a prepositive of open sabo dam using DEM

Load reduction mechanism analysis of energy dissipators at a prepositive of open sabo dam using DEM

Reinforcement basis design of Daigenta river sabo dam No. 1 based on result of decrepit research

Reinforcement basis design of Daigenta river sabo dam No. 1 based on result of decrepit research

Proposal of a new sabo dam construction method in a narrow area

Proposal of a new sabo dam construction method in a narrow area

Consideration on the capture situation of open type steel sabo dams

Consideration on the capture situation of open type steel sabo dams

Efektivitas Dan Kelengkapan Bangunan Sabo Di Sungai Togurara Daerah Gunungapi Gamalama

The lahar flow that occurred after the 2012 Gamalama Volcano eruption, leading to the eastern valley flowing downstream through the Togurara River to the center of Ternate City and Sultan Babullah Airport. To overcome the potential of lahar flow in the river since 2013 - 2016, several sabo dams and building facilities have been built. Based on the results of the calculation of deposits that potentially become lahar flows in 2016, the built-in capacity of the Sabodam has not been able to control the volume of sediment in the upstream of the river, then in the year 2017, 2018 constructed several additional Sabodam. In order to determine the effectiveness, feasibility and conditions of the completeness of Sabodam, is done field assessment on 25 ~ 27 September 2018, the method used was a mathematical approach based on sabo technology. The assessment was in the form of a field survey, simple measurements, interviews with the Sabodam management agency and local residents related to the lahar flow that had occurred. With the capacity of several additional Sabodams built in series, the average river bed slope was originally 9.09% to 6.83%. After the construction of Sabodam, the maximum lahar flow was once as high as 7 m, but now it decreases do 4.2 m. As the slope of the Togurara River slopes progressively, the lahar flow rate and its destructive power are reduced, so that Ternate City and Sultan Babullah Airport are spared from lahar disaster.Keywords: Lahar flow, sabodam, sabo technology, slope of riverbed, Togurara River.

Association of dissolved organic matter characteristics and trace metals in mountainous streams with sabo dams.

Metals undergo various processes transforming from one phase to another during transportation from head streams to oceans. The major chemical processes in the streams and rivers appear to be strongly dependent on dissolved organic matter (DOM). The mutualistic interactions between DOM and metals are important in determining the fate of many elements. We collected surface water samples from four stations along two mountainous streams in 2015 and analysed DOM quality and quantity and metal concentrations with the aim of understanding how changes in DOM characteristics are associated with dissolved metals along the stream with sabo dams. Both DOM and metal concentration were very low at the upstream site and did not show any significant correlation. However, sites within the dam vicinity (St.2 and St.3) had significantly high concentrations of manganese (Mn) and iron (Fe) which strongly correlated with molecular weight and aromaticity (> 0.6, p ≤ 0.01). Fe, Mn, copper (Cu) and aluminium (Al) significantly varied (p ≤ 0.05) downstream with highest average concentration for Al (17.7 ± 6.0 μg/L) and Cu (0.63 ± 0.3 μg/L). Cu had significant correlation with fluorescence components (fulvic-like, humic-like and protein like) and fluorescence index, while Fe significantly correlated to coloured DOM properties for all the sites. In the midstream section, strong correlations were exhibited by Fe, Cu, Zn and Mn whereas all metals did not show any significant correlation in the upstream site. Additionally, Cu, Mn and lead (Pb) showed strong correlation to DOM properties at the downstream site. The Fe to DOC and Mn to DOC ratios gave significant correlations with aromaticity, molecular weight and fulvic-like component at the midstream sections whereas Cu to DOC ratio lacked significant correlations to DOM at all the stations. Sabo dams enhanced Fe and Mn dissolution, while human activities in the downstream impacted Cu, Al, DOC, Mn and Fe stream concentrations. On the other hand, Fe and Mn were closely associated to DOM properties in regions of changing decreasing redox potential. The significant correlations presented by Mn, Fe and Cu with fluorescence index stresses the role of DOM heterogeneity in natural environments.

Evaluasi Kondisi Kerusakan Bangunan Pengendali Lahar di Sungai Krasak

The sabo dam located in the Krasak river area, which loads Mount Merapi eruptions, has been built more than 20 years old. This circumstance certainly affects the physical condition and function of the 23 sabos. Therefore, it is valuable to do a research which focuses on the damage sabo building to find out the necessary maintenance to take, so that the sabo building can be functioned properly. The method of the data collection is direct observation to the location. The results of the study indicate that 22 buildings are still in good category and 1 building is in a moderately damaged condition.Â

Proposal of Estimation Method for Debris Flow Potential Considering Eruptive Activity

An estimation method for debris flow potential is proposed to evaluate the possibility of the occurrence of rain-triggered debris flows. Sakurajima volcano has repeatedly erupted (Vulcanian type) and has continuously emitted volcanic ash at the Minamidake summit crater or Showa crater east of the summit since 1955, and debris flows have frequently occurred at rates of 10 to 111 events per year. Ground deformation associated with debris flows along the Arimura River were analyzed for the period from 2009 to 2016. Downward tilt (10–450 nrad) in the direction of the river and extensional strain (3–138 nstrain) were detected during occurrence of the debris flows. The tilt and strain changes were modeled using a point load caused by debris flow deposition beside a sabo dam. Depositional weights of individual debris flow events were estimated to range from 6 to 276 kt. The total weight of the debris flows was 2,154 kt, which is approximately 5% of the total weight of volcanic ash ejected from the craters during the study period. Debris flow potential (DFP) was defined as the difference in the volcanic ash deposits along the upper stream of the river (5% of the total) and the lower stream of the river, and the temporal change of the debris flow potential was investigated. When the debris flow potential reached a level of 0.4 Mt resulting from an increase in eruptive activity, debris flows frequently occurred or large debris flows were induced during rainy seasons. The concept of debris flow potential was applied to volcanoes in Indonesia as lahar potential. After the 2010 eruption at Merapi volcano, lahar potential, perhaps, quasi-exponentially decays during the dormant period. The lahar potential of Sinabung volcano complicatedly varies because of long-term eruptivity beginning in 2014.

Experimental study on debris flow impact load reduction by energy dissipators at front of open type Sabo dam

Experimental study on debris flow impact load reduction by energy dissipators at front of open type Sabo dam

Análisis del riesgo de erosión para la prevención de desastres en la caldera del Mt. Bawakaraeng, Indonesia

La erosión del suelo es un grave problema ambiental, pero su impacto en cárcavas como amenaza a la vida humana, ha sido poco estudiado en Indonesia. Los objetivos de esta investigación fueron analizar el riesgo de erosión en cárcavas para la mitigación de desastres y conocer la pérdida de suelo en la caldera del Monte Bawakaraeng. Se realizaron inventarios de desastres de flujos de escombros relacionados con cárcavas en la caldera de 2007 a 2017, se llevó acabo trabajo de campo y análisis de suelo. Para la pérdida de suelo se utilizó la Ecuación Universal de Pérdida de Suelo (USLE). Se determinó que existen 22 eventos de flujos de escombros relacionados a la erosión en cárcavas en los depósitos de sedimento. Los resultados mostraron que las partículas y la permeabilidad del suelo en la parte inferior de los depósitos podrían promover la erosión, en comparación con el sitio de la parte alta de la caldera. El análisis de riesgo de erosión reveló que 3.53 % del área estudiada tiene un tipo de erosión muy bajo; 12.87 % un nivel bajo; 64.06 % un nivel moderado; 0.06 % un nivel alto y 19.49 % un nivel muy alto. La construcción de sabo dam para controlar la erosión y sedimentación y el desarrollo de un sistema de alerta contra desastres debe hacerse de forma continua en el lugar.

Method to evaluate the effect of inclination angle of steel open-type check dam on debris flow impact load

Although the latest statistics indicate a decrease in the number of victims of natural disasters in Japan, the number of sediment disasters has increased. A countermeasure against natural disasters is provided by the installation of a steel open-type check dam (hereafter, open Sabo dam). The open Sabo dam is expected to capture boulders (more than 1.0 m in diameter) contained in debris flow of which boulders concentrate in front part. When a debris flow impacts an open Sabo dam, the large impact load on the steel pipes are caused by the impact of boulders under debris flow. Therefore, it is important to evaluate the impact of both boulders and the following soil and small gravels including fluid force of the open Sabo dam from the design point of view. Although an open Sabo dam has various shapes especially, the every open Sabo dams is evaluated by the same design method in Japan. It is necessary to propose the load evaluation method in the experiment scale in contrast with different shape of open Sabo dam. This article presents an experimental approach to determine the effect of the front inclination angle of steel open Sabo dams on the impact load. The debris flow impacts 1/40 scale models of steel open Sabo dams which are set in a flow channel flume, and the debris flow load is measured by using three load cells placed horizontally at the back of the Sabo dam model. Different front inclination angles are set for each Sabo dam models. The time history of the impact load is examined by comparing the loads corresponding to four kinds of dams, which are different from the front inclination angles, and decrease of impact load considering the buffering effect of driftwoods in debris flow.

Post-eruptive lahars at Kali Putih following the 2010 eruption of Merapi volcano, Indonesia: occurrences and impacts

Following the 2010 VEI 4 eruption of Merapi volcano, more than 250 lahars were triggered during two rainy seasons from October 2010 to March 2012. This high number of post-eruption lahars mainly occurred in the Kali (valley) Putih watershed and was mostly associated with high-magnitude rainstorms. A lahar occurring on January 8, 2011, caused significant damage to homes in several communities, bridges, sabo dams, and agricultural crops. The aims of this contribution are to document the impacts of lahars on the Kali Putih watershed and specifically (1) to analyze the lahar frequency during the period of 1969–2012 on an inter-annual and intra-annual basis and to determine the link between the volume of tephra and the frequency of lahars; (2) to detail the lahar trajectory and channel evolution following the January 8th lahar; (3) to map the spatial distribution of the thickness and geomorphic effects of the lahar deposit; and (4) to determine the impacts of the lahar on the infrastructure (sabo dams and roads) and settlements in the distal area of the volcano. The Kali Putih watershed has experienced 62 lahars, which represent 22% of all lahars triggered on 17 rivers at Merapi between 2010 and 2012. The main geomorphic impacts are: (1) excessive sedimentation in valleys, settlements and agricultural areas; (2) undercutting of the river banks by as much as 50 m, accompanied by channel widening; and (3) abrupt changes in the river channel direction in the distal area (15–20 km downstream of the volcano). About 19 sabo dams were damaged, and 3 were totally destroyed. Over 307 houses were damaged, and the National Road Yogyakarta–Semarang was regularly cut (18 times during approximately 25 days). Although the sabo dams on Kali Putih were originally constructed to protect distal areas from lahar damage, they had little effect on the 2010–2012 rain-triggered lahars. The underlying design of those dams along this river is one of the main reasons for the major destruction in this sector of the volcano’s lower slope. The catch basin capacity of the sabo dam was only 1.75 × 106 m3, whereas the total volume of the 2010–2011 lahars exceeded 5 × 106 m3. In order to prepare for future lahars, the government has invested in significant mitigation measures, ranging from structural approaches (e.g., building new sabo dams and developing an early warning system) to non-structural approaches (e.g., contingency and preparedness planning and hazard education).

Estimation of debris flow discharge coefficient considering sediment concentration

A sabo dam has a purpose to block the path of debris flow. However, when overflow occurs, a sabo dam works as a weir, a vertical obstruction, where the fluid must flow over. Many empirical formulas and discharge coefficients for weirs relating flow depth to discharge have been proposed to calculate overflow discharges. However, only a few studies about overflow discharge coefficients are available in the case of debris flow. In this paper, experiments and numerical simulations were done to estimate debris flow discharge coefficients by considering the sediment concentration. In the numerical simulation, a complete overflow equation and a free overfall equation were implemented to calculate debris overflow discharges at a sabo dam. To determine the discharge coefficients for each equation, single factor regression analysis was used. Laboratory experiments were done to calibrate and to compare with the simulation. Study results showed that the discharge coefficients increase as the sediment concentration increases. This finding suggests debris flow discharge coefficients are derived to calculate the debris overflow discharges at a sabo dam.

Dissolved organic matter characteristics along sabo dammed streams based on ultraviolet visible and fluorescence spectral properties.

Changes in dissolved organic matter (DOM) characteristics were investigated in two mountainous streams with closed-type sabo dams. Surface water was collected from four stations along the two mountainous streams and analyzed using ultraviolet-visible spectrophotometry and excitation-emission fluorescence matrix (EEM) methods. Optical properties of DOM indicated an increase in molecular weight and aromaticity at stations near the sabo dams. Average spectral ratio values were low before and after the dam (i.e., < 0.72) compared to other sections of the stream. Specific ultraviolet absorbance (SUVA254) increased in the vicinities of the dams. While chromophoric DOM characteristics from two sites were influenced by the dam, fluorescence components, however, did not show notable changes around dams. Instead, the three chromophoric components distinguished by EEM-parallel factor analysis, that is, humic-like (C1 and C2) and protein-like (C3) increase along the stream. Fulvic-like component (C1) had a high fluorescence intensity at all stations; all the three components were more abundant in the downstream section. Chromophoric DOM properties varied along the stream based on alterations in molecular size and aromaticity. Using multivariate analysis, the studied sites were grouped into three clusters related to sabo dams and other activities. We conclude that sabo dams modify DOM characteristics which influence the behavior of DOM transported along the stream.

Insights into lahar deposition processes in the Curah Lengkong (Semeru Volcano, Indonesia) using photogrammetry-based geospatial analysis, near-surface geophysics and CFD modelling

Semeru Volcano is an active stratovolcano located in East Java (Indonesia), where historic lava flows, occasional pyroclastic flows and vulcanian explosions (on average every 5min to 15min) generate a stock of material that is remobilized by lahars, mostly occurring during the rainy season between October and March. Every year, several lahars flow down the Curah Lengkong Valley on the South-east flank of the volcano, where numerous lahar studies have been conducted. In the present contribution, the objective was to study the spatial distribution of boulder-size clasts and try to understand how this distribution relates to the valley morphology and to the dynamic and deposition dynamic of lahars. To achieve this objective, the method relies on a combination of (1) aerial photogrammetry-derived geospatial data on boulders' distribution, (2) ground penetrating radar data collected along a 2km series of transects and (3) a CFD model of flow to analyse the results from the deposits. Results show that <1m diameter boulders are evenly distributed along the channel, but that lava flow deposits visible at the surface of the river bed and SABO dams increase the concentration of clasts upstream of their position. Lateral input of boulders from collapsing lava-flow deposits can bring outsized clasts in the system that tend to become trapped at one location. Finally, the comparison between the CFD simulation and previous research using video imagery of lahars put the emphasis the fact that there is no direct link between the sedimentary units observed in the field and the flow that deposited them. Both grain size, flow orientation, matrix characteristics can be very different in a deposit for one single flow, even in confined channels like the Curah Lengkong.

Slope management utilizing the historical masonry Sabo dams (Sunadome in Japanese)

広島県福山市には, 江戸時代の備後福山藩によって構築された砂防堰堤“砂留 (すなどめ)”があり, 補修されながら今日も渓流保全機能を有している。現在, それら砂留の周辺は環境整備とともに市民の憩いの場となっており, 周辺の環境整備がなされている。環境整備にはボランティア活動により, 森林保全を行うことで斜面の安定に係る維持管理が継続されている。本稿は, このような福山市・堂々川周辺で取り組まれている斜面環境全体の保全活動から, 長期に渡り扱われてきた歴史的構造物及びその周辺環境の管理のあり方を学び, “歴史的構造物の維持管理”を斜面維持管理の活動という視点で考察した。

The effect of front inclination angle of steel open type Sabo dam on debris flow impact load

The effect of front inclination angle of steel open type Sabo dam on debris flow impact load

Safety verification of steel open type Sabo dams against large scale debris flow

Safety verification of steel open type Sabo dams against large scale debris flow

Direct field observations of massive bedload and debris-flow depositions in open check dams

Sediment detention basins, also called SABO dams, are key facilities in flood protection systems of mountain catchments, specifically in torrents prone to massive bedload transport or debris flows. A better understanding of the processes generating sediment trapping is required to optimize their functioning. Two monitoring stations have been implemented in the French Alps on two torrents: the Manival (Saint-Nazaire-Les-Eymes) and the Claret (Saint-Julien-Mont-Denis). Time-lapse photos show an event depositing 10,000 m3of debris flow in a basin in less than six minutes and several events partially filling the other basin with gravel, impairing its capacity to store debris flows later. After a presentation of the catchments, this paper qualitatively analyzes the dynamics of the depositions. It highlights and stresses the consistency and differences between bedload and debris-flow deposition. Overall, despite clear differences of geomorphic activity, deposits tend to fill the trap basins just enough to enable the sediment transport continuity reestablishment through the basin. The open check dams thus play a role only provided that this continuity precondition is completed. These observations enhance our comprehension of massive sediment trapping in torrents and our capacity to better adjust trap maintenance and design to the objective sought in each site.